1. Field of the Invention
The present invention generally relates to an oscillating shuttle of a sewing machine and relates particularly to the art of preventing a needle-thread loop from being bitten by the oscillating shuttle.
2. Related Art Statement
There is known a lock-stitch sewing machine which employs, as a thread-loop catcher including a hook portion for hooking or catching a loop of a needle thread conveyed by the eye of a sewing needle, and locking the needle-thread loop with a bobbin thread, a rotary hook which is fully rotatable at a high speed. There is also known a twin-needle sewing machine which employs, for performing bar-tack stitching on thick work sheets, two oscillating shuttles each of which has a driver which drives a shuttle body and includes a needle guard for preventing a corresponding sewing needle from being excessively moved toward the shuttle during its sewing operation. Since, in an oscillating shuttle, a loop of a needle thread is released from a hook portion at an early timing, the needle thread is easily drawn up and the needle-thread loop is well tightened. An oscillating shuttle includes a first shuttle race member which is attached to a bed of a sewing machine such that the first race member takes a horizontal attitude; a second shuttle race member which is detachably attached to the first race member to provide a shuttle race; a shuttle body which is accommodated in an inner space of the shuttle race; and a driver which drives or half-rotates the shuttle body in opposite directions.
FIG. 10 shows a known oscillating shuttle 100 which includes a first shuttle race member 102; a second shuttle race member 103 which is detachably attached to the first race member 102 to provide a shuttle race having a substantially annular guide groove 107 at an interface where the second race member 103 is attached to the first race member 102; a shuttle body 104 which has a generally semi-circular shape as viewed from its front side and which includes a generally semi-annular guided portion 104b which is provided over a substantially entire outer surface thereof and which has a generally rectangular cross section; and a driver (not shown) which half-rotates the shuttle body 104 in opposite directions in synchronism with upward and downward movements of a sewing needle 111, while the guided portion 104b is slideably guided by the guide groove 107.
The known oscillating shuttle 100 is operated such that, when the sewing needle 111 is moved up by a small distance from its lowest position, the needle thread 112 conveyed by the eye of the needle 111 is hooked or caught by a hook portion 104a of the shuttle body 104 being rotated in a forward direction and, when the shuttle body 104 is generally half rotated in the forward direction, a widened loop 112a slips from the hook portion 104a. Then, as the shuttle body 104 is rotated in a backward direction opposite to the forward direction, and as a needle-thread take-up is substantially simultaneously moved up, the needle-thread loop 112a is tightened up while being locked with a bobbin thread supplied from a bobbin (not shown) accommodated in a bobbin case (not shown) supported by the shuttle body 104. The needle-thread loop 112a is passed between the driver and a rear end portion of the shuttle body 104 opposite to the hook portion 104a, and is drawn up through a throat plate 110, so that a lock stitch is formed on thick work sheets W1, W2.
In the case where the known oscillating shuttle 100 is used for sewing, using a thick needle thread, the plurality of thick work sheets W1, W2 (e.g., denim sheets) superposed on each other, the shuttle body 104 starts its reverse rotation at a timing at which the needle-thread loop 112a widened by the hook portion 104a slips from the same 14a. Substantially simultaneously, the needle-thread take-up starts its upward movement and accordingly the needle-thread loop is tightened. However, since the superposed thick work sheets W1, W2 exert a great resistance to the needle thread 112 being moved therethrough, the needle-thread take-up may fail to draw up a sufficient length of the needle thread 112. That is, as shown in FIG. 10, a lower end portion of the needle-thread loop 112a may be caught by a tail portion of the shuttle body 104 because the tightening of the loop 112 delays when the tail portion of the shuttle body 104 is moved back through an upper opening formed in respective upper end portions of the first and second race members 102, 103.
Thus, the lower end portion of the needle-thread loop 112a is forced to enter the spaces defined by opposite surfaces of the guided portion 104b of the shuttle body 104 and opposed surfaces of the first and second race members 102, 103 which cooperate with each other to define the guide groove 107. Since those spaces are very narrow, the loop 112a is bitten fast, and breaks.